Expansion valves are used to control or meter the flow of refrigerant to an evaporator in an air conditioning system, to provide a refrigerant flow rate into the evaporator that approximately matches the refrigerant flow exiting the evaporator. An expansion valve typically permits fluid flow from the inlet to the outlet during normal operation of the air conditioning system, where the fluid at the inlet is typically at a higher pressure than the fluid at the outlet.
Electronically operated step motor flow control valves are used for the precise control of liquid refrigerant flow as expansion valves referred to herein as EEVs. In operation of an EEV, an electronic controller sends signals to the step motor based on information provided to the controller by sensors. Synchronized signals to the motor provide discrete angular movement, which translates into precise linear positioning of the valve piston. The EEV controls the flow of refrigerant entering the evaporator in response to signals sent by the controller.
These signals are calculated by the controller from sensor inputs. A set of sensors, either two temperature sensors or a pressure transducer and a temperature sensor, are used to measure superheat. Typical control is based on superheat setpoint but an additional temperature sensor may be used to measure discharge water or air temperature. This air or water temperature is controlled directly, as long as superheat remains at a level to prevent floodback. The ability of the EEV to control the amount of refrigerant in the evaporator to allow reaching discharge setpoint while preventing floodback makes the EEV the ideal expansion device for most air conditioning, chiller, environmental chamber, and refrigeration applications. Some EEV controllers can be programmed to follow unique control algorithms making the EEV especially useful for many diverse applications.